floating watermoss; Salvinia natans
A small aquatic fern that floats on still water; the name comes from the resemblance of its leaves to Japanese pepper (山椒).
The pond is covered with floating watermoss.
Katakana spelling is standard for this plant name; usually written in kana.
Kanji spelling is rare and mainly encountered in botanical contexts.
The name is a compound of 山椒 (sanshō, Japanese pepper) and 藻 (mo, water plant), referring to the pepper-like scent of the leaves when crushed.